Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B6/13—Integrated optical circuits characterised by the manufacturing method
  • G02B6/134—Integrated optical circuits characterised by the manufacturing method by substitution by dopant atoms
  • G02B6/1345—Integrated optical circuits characterised by the manufacturing method by substitution by dopant atoms using ion exchange
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B6/126—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind using polarisation effects

Definitions

• Optical wave guide devices fabricated by the Proton Exchange (PE) method provide some unique qualities.
• the process of proton exchange increases the refractive index only in extraordinary axis and thus will only guide one polarization state. The other polarization state is unguided and is eventually eliminated.
• This quality of Proton Exchange devices makes them naturally very high performance polarizers (60 dB or more). In addition, this quality makes them very attractive for use in Multiple Function Chips (MFCs) used in construction of fiber optic gyros (FOGs).
• MFCs Multiple Function Chips
• FIGURE IA shows a schematic diagram of a proton exchange polarizer with crosstalk.
• a proton exchange polarizer 10 includes a LiNbO 3 or LiTaO 3 material forming an optically transmissive substrate 16.
• the proton exchange polarizer 10 further includes a glass ferrule 20 as an input coupling for an optical fiber 12 and a glass ferrule 22 coupled to an output fiber 14.
• the optical fiber 12 receives light comprised of both a TE mode 24 and a TM mode 26.
• the TE mode 24 includes the solutions of Maxwell's equations with symmetric boundary conditions for an optical wave propagating within the waveguide (i.e.
• LiNbO3 at both sides of the waveguide and the TM mode 26 includes the solutions of Maxwell's equations with non-symmetric boundary conditions for an optical wave propagating within the waveguide (i.e. LiNbO3 at one side of the waveguide and air at the opposing side of the waveguide).
• TE mode light 32 is substantially guided by a proton exchange wave guide 18 through the optically transmissive substrate 16.
• the TM mode 26 becomes unguided TM mode light 30.
• the TE mode 24 becomes guided TE mode light 32 by the proton exchange wave guide 18.
• Unguided TM mode light 30 propagates through the optically transmissive substrate 16. A portion of the unguided TM mode light 30 from the polarizer escapes. An angle of reflection 28 may be determined by the dimensions of the particular embodiment, specifically the distance between the glass ferrules 20 and 22.
• the TM mode unguided light 30 is reflected as indicated by light 36 from a bottom 17 and sides of the substrate 16 and exits the substrate through fiber 14.
• the reflected unguided TM mode light 36 is unwanted in various applications such as fiber-optic gyros.
• the invention provides a proton exchange polarizer where cross- coupling of unwanted modes of light is reduced with an integrated spatial filter.
• An optically transmissive substrate such as a substrate created from LiNbO 3 or LiTaO 3 has side surfaces which reflect unguided TM mode light. The light originates from an input fiber. The input fiber is connected to the substrate at one end and an output fiber is connected to receive guided TE mode light at the opposite end. The sides of the substrate couple the unguided TM mode light to the output fiber. This coupling is undesirable in various polarizer applications such as those used in fiber-optic gyros. The extinction ratio of the substrate is improved by the incorporation of a spatial filter.
• the spatial filter is positioned at the primary reflection position of the light with respect to the sides of the polarizer. To improve extinction further, the spatial filter can also be located at secondary reflection points in another alternate embodiment.
• the spatial filter is positioned within the substrate or at the sides of the substrate, depending on whether the barrier was created by physical or chemical methods such as saw cutting, etching, diamond machining, micro-machining, or laser-machining.
• the spatial filter acts to block the propagation of the unguided TM light.
• FIGURE IA schematically shows a proton exchange polarizer side view illustrating a crosstalk/modulator mechanism formed in accordance with the prior art
• FIGURE IB schematically shows a proton exchange polarizer top view illustrating the crosstalk/modulator mechanism; formed in accordance with the prior art
• FIGURES 2A, B show side and top views of a filter formed in accordance with an embodiment of the present invention
• FIGURE 3 A shows a perspective view of a spatial filter created by cutting a slot in the sides of the substrate
• FIGURE 3 B shows a side view of the spatial filter of FIGURE 3 A
• FIGURE 4 shows a isometric view of the substrate with grooves in the side wall of the substrate.
• FIGURE 5 shows an anti-reflective coating on the sides of a substrate used to absorb unguided TM or light in the anti-reflective layer.
• FIGURES 2A, B show a proton exchange polarizer 11 with an integrated spatial filter 34 located in the substrate 16a.
• the substrate 16a couples a fiber 12 with ferrule 20 to fiber 14 to ferrule 22.
• the substrate 16a incorporates a proton exchange wave guide 18.
• the TM mode unguided light 30 propagates through the light conducting substrate 16a but is blocked by spatial filter 34 incorporated into the substrate 16a.
• the spatial filter 34 prevents reflected light from coupling back into the output fiber 14 by blocking the propagation of the light wave.
• the barrier, or the spatial filter 34 may be advantageously made by a number of processes including physically depositing the spatial filter 34 into the substrate 16a.
• the substrate may be saw-cut to create a void in the substrate 16a impeding the propagation of the unguided TM mode light 30.
• the side may be diamond machined, etched, micro- machined or laser-machined. Alternatively, the surface may simply be scratched or similarly damaged to provide spatial filters in the propagation path of the TM mode unguided light 30.
• the reflected TM mode light 30 is thus substantially removed by creating a spatial filter 34 in the sides 39 of the substrate 16a.
• the spatial filter 34 or barrier incorporated into the substrate 16a any reflected TM light 30 will be substantially blocked.
• FIGURES 3A, B shows a spatial filter created by a dicing saw.
• FIGURE 3A shows an isometric view of the substrate 16 with three slots 38a, 38b and 38c. Slots 38a and 38c are used to attenuate the secondary reflections and 38b is intended to remove the primary reflection.
• the side of the substrate 16 is shown with cuts made across the entire height of the substrate 16. The side view shows the slots 38a, 38b, and 38c cut into the side of the substrate 16 attenuating the primary and secondary reflections.
• FIGURE 4 shows micro-etched grooves 42 in a substrate 76.
• the micro-etched groves 42 are formed on vertical sides 78 of the substrate 76 substantially at about a 45° angle as referenced to an incoming beam of light. In this way, reflected light is rejected at an angle of about 90° off the incident beam.
• the grooves may be formed by chemical etching or by mechanical abrasion (saw cuts, grinding, etc.).
• FIGURE 5 shows an alternate embodiment of the present invention using an antireflection and absorbing layer 44 at the sides of a substrate 86 so that there are no reflections from the sides of substrate 86.
• Antireflection layers may be formed by deposition of dielectric materials such as Magnesium Fluoride, silicon, or polymers.
• the present invention may be combined with a spatial filter located on the bottom surface of the substrate, such as that shown and described in U.S. Patent No. 5,475,772, which is hereby incorporated by reference.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Integrated Circuits (AREA)
• Optical Couplings Of Light Guides (AREA)

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• 2007
  • 2007-09-28 US US11/864,742 patent/US7711216B2/en active Active
• 2008
  • 2008-10-22 WO PCT/IB2008/003891 patent/WO2009109806A1/en active Application Filing
  • 2008-10-22 JP JP2010526394A patent/JP2012506561A/ja active Pending
  • 2008-10-22 EP EP08873118A patent/EP2193393A4/de not_active Withdrawn

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